Biomedical subjects

Helmut Prior

Publications and source records attributed to Helmut Prior.

8 recordsLinked to original sources

PubMed2005

Effects of the acoustic environment on learning in rats.

Although noise of moderate intensity is commonly present during experiments on animal learning and memory, its effects have usually not been considered. The present study investigated how differences in the acoustic environment affect learning and memory under otherwise identical conditions. Genetically defined rats learned a complex maze in noise of moderate intensity (70 dB) or in quiet. Noise had a profound effect on learning and behaviour. Noise-exposed rats made fewer errors, explored less and finished their trials sooner. Results show that the acoustic environment is an important variable in studies with animal models of learning and memory. This might explain why differences in learning and behavioural scores occur across laboratories even when the same rodent strains and apparently identical experimental protocols are used. As the effects probably rely on neurotransmitter systems common in vertebrates, similar effects can be expected in other species including humans.

Acoustic Stimulation↗

PubMed2005

Filling-in with colour: different modes of surface completion.

We investigated the figural dynamics of filling-in processes in figures with more than one possible figure-ground organisation. Using a central disk and two concentric rings as well as similar stimuli consisting of three nested squares or parallel stripes, we tested for filling-in with different equiluminant colour combinations. We observed four modes of filling-in: First, in most of the cases, the inner ring assumed the colour of the central disk and outer ring (M1). Second, the central disk became filled-in with the colour of the inner ring, without any colour change on the outer ring (M2). Third, in a first step, the colour of the inner ring spread onto the central disk; then, in a second step, the colour of the outer ring spread over the whole stimulus (M3). This two step filling-in process has not been reported so far. Fourth, a mode (M4) was sometimes observed that was characterised by the central disk and outer ring assuming the colour of the inner ring. Thus, colour filling-in or colour spreading proceeded both in a centripetal (periphery to fovea) as well as a centrifugal direction. The colours red and yellow proved to be stronger inducers than blue and green. Conversely, the latter colours became filled-in more easily than the former. The filled-in colour was always that of the inducing stimulus, i.e., there was no colour mixture. This suggests a long-range, neural process underlying filling-in under these conditions.

Adult↗

PubMed2004

Visual lateralization and homing in pigeons.

The aim of our study was to analyse the components of visual lateralization in pigeon homing, a large-scale spatial task. In a series of 13 releases, birds were tested as binocular controls or monocularly with the right or left-eye covered. Occlusion of either eye had a significant effect on initial orientation and homing performance. Vanishing bearings were deflected to the side of the open eye, vanishing intervals were longer, and homing speed was reduced. These parameters were affected to a different degree. Initial orientation was markedly lateralized, with birds using their right-eye deviating less from the mean of control birds and showing significantly less variance. One minute after release, the deviation and variance were similarly large in both monocular groups. However, while the right-eyed birds improved their performance until leaving the release site, the left-eyed birds failed to do so. Vanishing intervals were similar in both monocular groups, but homing speed was reduced to a lesser extent in pigeons using the right-eye. The degree of lateralization varied across different releases, but superiority of the right-eye/left hemisphere prevailed. Lateralization did not depend on familiarity with the release site. This suggests that the crucial processes involved the eyes, but did not depend on visual memory of landscape features at the release site. Results reveal, for the first time, asymmetries of directional orientation as an essential component of lateralized homing performance. As likely mechanisms we suggest hemispheric differences in magnetic compass orientation and in the adjustment to optic flow.

Age Factors↗

PubMed2004

Exploration, emotionality, and hippocampal mossy fibers in nonaggressive AB/Gat and congenic highly aggressive mice.

AB/Gat mice and congenic mice bred for high aggressiveness (CS/ag) were tested for exploratory behavior in novel situations and anxiety-related behavior, using an open-field test and the elevated plus-maze test. Subsequently, the size of hippocampal mossy fiber terminal fields was evaluated. Considerably higher exploratory activity was found in nonaggressive mice, whereas aggressive mice exhibited more anxiety-related behavior. Larger intra- and infrapyramidal mossy fiber terminal fields (IIP-MF) and a larger hilus were found in the highly aggressive strain. Within the nonaggressive AB/Gat strain, larger IIP-MF were correlated with higher exploratory behavior and lower anxiety in the plus-maze test. Within the aggressive strain, no individual correlations between hippocampal morphometry and behavior were found. The results corroborate the "ecotype hypothesis," which suggests that mice of subpopulations with highly aggressive males tend to display reduced exploratory behavior. The findings support the view that genetic factors involved in aggressive behavior also affect hippocampal connectivity. However, our results do not support the hypothesis that a higher level of aggressiveness is necessarily related to smaller IIP-MF.

Aggression↗

PubMed2002

Effects of monocular viewing on orientation in an arena at the release site and homing performance in pigeons.

Orientation and homing performance of pigeons with the left or right eye occluded were assessed in an arena at the release site and during the subsequent homing flight. Three release sites near Pisa, Italy, were used. Compared to binocular controls, monocular birds showed a bias in orientation towards the side of the viewing eye. In the arena, this bias was considerable and the mean deviation corresponded to the angle of the optical axis, suggesting a systematic error in visual representation during directional orientation. During flight after leaving the arena the directional bias decreased and the homeward orientation increased. While there was a slight lateralization of overall homing performance in favour of the right eye, there was no lateralization in directional orientation in the arena or at vanishing. Our results show that navigational mechanisms in either brain hemisphere profit from information obtained before take off and while flying over the release site. The existence and degree of lateralization is discussed in comparison to other studies that investigated homing under monocular viewing conditions.

Animals↗

PubMed2002

Lateralization of magnetic compass orientation in a migratory bird.

Lateralization of brain functions, once believed to be a human characteristic, has now been found to be widespread among vertebrates. In birds, asymmetries of visual functions are well studied, with each hemisphere being specialized for different tasks. Here we report lateralized functions of the birds' visual system associated with magnetoperception, resulting in an extreme asymmetry of sensing the direction of the magnetic field. We found that captive migrants tested in cages with the magnetic field as the only available orientation cue were well oriented in their appropriate migratory direction when using their right eye only, but failed to show a significant directional preference when using their left eye. This implies that magnetoreception for compass orientation, assumed to take place in the eyes alongside the visual processes, is strongly lateralized, with a marked dominance of the right eye/left brain hemisphere.

Functional Laterality↗

PubMed2002

Effects of predictable and unpredictable intermittent noise on spatial learning in rats.

The effects of predictable (periodic) and unpredictable (aperiodic) intermittent noise of moderate intensity (68 dB) on the learning of a complex T-maze by genetically defined rats were investigated. In Experiment 1, three groups (n=8) of rats learned a multiple T-maze, one group under control conditions, one group with predictable intermittent noise and one group with unpredictable intermittent noise. Results showed a profound effect of noise on learning and behavioural scores. Noise-exposed animals made less errors, finished their trials sooner and explored less. There was no difference between predictable and unpredictable noise. Further tests, during which formerly noise-exposed groups learned a new route under control conditions (Experiment 2) or the former controls learned a new route with noise (Experiment 3), suggest that the effects of noise on learning were caused by an effect of noise on memory formation and/or retrieval, rather than by long-term shifts in behavioural strategies.

Analysis of Variance↗

PubMed2002

Orientation and lateralized cue use in pigeons navigating a large indoor environment.

The pigeon's use of different visuo-spatial cues was studied under controlled laboratory conditions that simulated analogous aspects of a homing situation. The birds first learned the route to a goal that was not visible from the starting location, but became visible as it was approached. Birds could orientate within a mainly geometric global reference frame, using prominent landmarks within their range, or by 'piloting' along local cues. After learning the route, the birds were tested from familiar and unfamiliar release points, and several aspects of the available cues were varied systematically. The study explored the contribution of the left and right brain hemispheres by performing tests with the right or left eye occluded. The results show that pigeons can establish accurate bearings towards a non-visible goal by using a global reference frame only. Furthermore, there was a peak of searching activity at the location predicted by the global reference frame. Search at this location and directedness of the bearings were equally high with both right and left eye, suggesting that both brain hemispheres have the same competence level for these components of the task. A lateralization effect occurred when prominent landmarks were removed or translated. While the right brain hemisphere completely ignored such changes, the left brain hemisphere was distracted by removal of landmarks. After translation of landmarks, the left but not the right brain hemisphere allocated part of the searching activity to the site predicted by the new landmark position. The results show that a mainly geometric global visual reference frame is sufficient to determine exact bearings from familiar and unfamiliar release points. Overall, the results suggest a model of brain lateralization with a well-developed global spatial reference system in either hemisphere and an extra capacity for the processing of object features in the left brain.

Animals↗